In sanctioned drag racing, there are certain race classes in which the goal of a drag racer is to run a distance, as close as possible, to a predetermined time. A racer who runs the distance faster than this predetermined time has that run disqualified. Since it is standard practice for racers to race with the highest possible rate of acceleration and highest top speed with a car that can achieve speeds considerably greater than the standard speed for the class in which the car will run, some type of throttle valve limiting device customarily is used to slow the car to the standard speed of the class of the car.
Typically, the throttle valve control system employed in racing engines for this purpose comprises a gas controlled piston/cylinder device installed in the throttle linkage between the accelerator pedal and the carburetor, which controls the throttle valve. The linkage from the accelerator pedal is connected to the cylinder of the piston/cylinder device and the linkage from the carburetor is connected to the piston rod mounted to the piston and extending from the cylinder. When the piston/cylinder assembly is retracted, the throttle linkage is at its standard length for normal operation of the carburetor. However, when the piston/cylinder assembly is extended, the throttle linkage moves the carburetor valve toward its closed position.
A source of compressed gas, typically CO.sub.2, is delivered into the cylinder chamber, which forces the piston rod to retract into the cylinder, allowing the accelerator pedal linkage to control the carburetor in a conventional manner, i.e., as if the piston/cylinder device were not installed in the system. Thus, upon full depression of the accelerator pedal, the throttle valve opens completely, and upon release of the accelerator pedal, the throttle valve closes.
At the start of a race, the source of compressed gas is communicated with the cylinder to retract the piston so that upon depression of the accelerator pedal the throttle valve opens completely. After a specified time from the start of the race, typically a few seconds, the throttle valve control system vents the compressed gas in the cylinder to the atmosphere which releases the pressure within the cylinder chamber acting against the piston. A spring biasing means attached to the end of the piston rod urges the piston rod from the cylinder, thus causing the carburetor linkage to close the throttle valve. After another predetermined period of time, the throttle valve control system reestablishes communication between the compressed gas source and the cylinder, causing the piston rod to retract into the cylinder and, consequently, the throttle valve to open back up. Throttle valve control systems of this type are not designed to cause the race car to slow down, but rather to have the effect of limiting the rate of acceleration of the car, allowing the racer to achieve a desired race time.
However, throttle valve control systems of this type can cause several problems. First, it is difficult to control the degree of throttle valve closure when the flow of compressed gas to the cylinder is terminated and the gas of the cylinder is vented to the atmosphere. In practice, the throttle valve moves toward a closed position and continues to move toward its closed position until the flow of compressed gas to the cylinder is reestablished. To limit the extent of throttle valve closure, some systems utilize an adjustment bolt screwed into the back of the cylinder, which bolt connects the linkage from the accelerator pedal to the cylinder. This bolt adjusts the position of the cylinder relative to the accelerator pedal and therefore adjusts the overall length of the throttle linkage between the cylinder and the accelerator pedal and, thereby limits the extent to which a fully extended piston rod can cause the throttle valve to close. However, because there is only a limited amount of travel of the accelerator pedal and the cylinder when moved by the accelerator pedal, such an arrangement typically has little or no effect in racing applications wherein the compressed gas source is reestablished to the cylinder prior to the piston rod fully extending from the cylinder. In addition, the throttle linkage has to be loosened from the cylinder in order to adjust the bolt, an adjustment procedure that is complicated.
Second, prior art throttle limiting designs are not easily adjustable to be adapted to variable racing conditions, such as weather and track conditions. Another problem with prior art systems is that, upon recharging the cylinder with compressed gas, the throttle valve opens quickly due to the force of the compressed gas retracting the piston. Rapid throttle opening can cause the tires to spin and the vehicle to become unstable.
Accordingly, a heretofore unaddressed need exists for a throttle valve control system that can control the degree of throttle closure upon expansion of the throttle linkage, that includes a simple adjustment mechanism for adapting the throttle valve control system to variable racing conditions, and that can control the rate of throttle reopening upon expansion of the throttle linkage. It is to the provision of such a throttle valve control system that the present invention is primarily directed.